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Eight Easy Steps To Better Spraying

Susan Davis | Feb 01, 1998

You don't have to buy a $50,000 sprayer to do a better job of applying pesticides. A few inexpensive tools, coupled with a generous amount of caution, can help you hit the target with just the right amount of chemical every time.

Here are a few suggestions from Erdal Ozkan, Ohio State University extension ag engineer, and Larry Schulze, University of Nebraska extension pesticide coordinator.

1) Use a wind meter.

Someday, weather conditions will be automatically recorded when you hop in the sprayer or tractor cab. Until then, a wind meter could keep you out of court, says Ozkan.

Always record the wind speed before applying pesticides, he suggests. Dwyer Instruments, Michigan City, MI, sells wind meters for less than $20. A more precise meter can cost over $100, but will be more reliable and last longer, Ozkan says.

Two-thirds of pesticide non-compliance complaints brought to the Ohio Department of Agriculture are due to spray drift, he adds.

"The biggest reason we have spray drift complaints is because pesticide application is done at times when wind speed is excessive."

2) Watch for erratic conditions.

Severe drift can also happen at low wind speeds. Wind is generally recognized as an important factor, but vertical movement is often overlooked, Schulze points out.

Temperature inversions occur when cool air near the soil surface is trapped under a layer of warmer air above. Trapped spray droplets may fall slowly or be suspended and move several miles to susceptible crops.

Smoke from a fire is one way to know if there's a temperature inversion. If smoke moves horizontally close to the ground, don't spray near susceptible crops.

3) Pay attention to humidity.

Low relative humidity and/or high temperatures cause faster evaporation of spray droplets and a higher drift potential. Pesticides evaporate at different rates. Use formulations and adjuvants that reduce evaporation.

As a general rule, spray conditions are ideal if the humidity is above 70%. A relative humidity below 50% warrants special attention.

4) Pay attention to boom height.

Operating the boom as close to the sprayed surface as possible while staying within the manufacturer's recommendation is a good way to reduce drift. A wider spray angle allows the boom to be placed closer to the target.

5) Use low-drift nozzles.

Nozzles such as the TurboDrop and Turbo TeeJets deliver smaller, more effective droplets and still reduce drift potential.

6) Invest in accurate gauges.

Ozkan prefers a glycerine-filled pressure gauge because its internal parts won't rust. Also, taking readings off a glycerine-filled gauge is easier because the needle doesn't vibrate as wildly as in other gauges, he says.

In addition to the gauge in the cab or near the pump, use another gauge to measure the exact pressure at the nozzle, Ozkan advises. Check the pressure at different boom sections; pressure always drops across the boom. A pressure drop changes both the flow rate and droplet size.

Even if you have perfect spraying conditions, you won't get satisfactory results unless the sprayer is calibrated correctly.

A University of Nebraska field survey of 103 private applicators showed that only 30% were applying herbicides within 5% of the intended application rate. Another 26% over-applied herbicides during a single application, and 44% underapplied herbicides.

The time spent calibrating, or the cost of adding new components, can be rapidly recovered with improved application accuracy, Schulze says.

To learn more, see the University of Nebraska's Pesticide Education Resources Web site. The site offers pesticide application information galore.